The 31p NMR technique enables signals from phosphates in tissues, cells or granules to be monitored directly. The measurement of internal pH using ATP gamma or Pi is being tested quantitatively and improved probe molecules are being developed to measure delta pH and trans-membrane potential delta psi) in cell ghosts with intact transport systems. Carbon-13 NMR studies of 13C NMR studies of 13C enriched metabolites are also being pursued.